It is known, for example from EP 1 168 913, to provide a system for extracorporeal organ perfusion in which a human or non-human organ can be preserved, for example prior to transplant into a patient. The system typically comprises a reservoir for perfusion fluid (or perfusate), which may be blood or another perfusion solution, and a circuit for circulating the fluid through the organ. The circuit typically also comprises an oxygenator or other device for adding oxygen, carbon dioxide, or other substances into the blood, from a source which typically comprises a pressurized gas cylinder.